Eukaryotic hosts are infected by a variety of viral pathogens, including RNA viruses. However, very little is known about host proteins (factors) that are used or recruited by viral pathogens to carry out viral processes. The objective of this research is to identify genetic loci in the model host Arabidopsis thaliana that are required for systemic infection by the viral pathogen tobacco etch virus (TEV). TEV is a positive sense RNA virus that is a member of the picornavirus superfamily. The Arabidopsis/TEV system will take advantage of the many genetic and molecular tools developed by the Arabidopsis community and the properties of TEV that allow it to maintain foreign genes, such as beta glucuronidase and jelly fish Green Fluorescent Protein, during systemic infection of hosts. The proposed research will use genetic screens and selections to identify Arabidopsis mutants that do not support systemic TEV infection. These mutants will be characterized by genetic and cell biology methods, and the cloning of the corresponding genes will be initiated. The cloning of host factor genes will facilitate our understanding of how viruses and their hosts interact at the molecular and cellular levels.